This proposal describes a five-year training program for development of a research career in cardiovascular developmental biology. The candidate is a clinical associate in pediatric cardiology at the Children's Hospital of Philadelphia (CHOP), with an M.D.-Ph.D. in molecular biology. He has extended his training engaged in intensive basic science research supported by the Ruth L. Kirschstein National Research Service Award (T32), and is currently supported by the Department of Pediatrics Child Health Research Career Development Award (K12). The proposed research will enhance our understanding of congenital heart disease. It will be carried out under the mentorship of Jonathan Epstein, M.D. a recognized leader in the field of cardiac development. He is a professor of Medicine, and the scientific director of the University of Pennsylvania Cardiovascular Institute (CVI). He has mentored numerous Postdoctoral fellows and graduate students. An advisory committee of talented clinician-scientists has been assembled to offer guidance in career development and science. The environment of CHOP and the CVI provides extensive resources, collaborations, core facilities and intellectual expertise. This is an ideal training setting to develop a skill set in order to transition to an independent career as a physician-scientist. Participation in didactic courses and faculty professional development seminars will enhance the educational success of the program. Congenital heart disease (CHD) is the most common life-threatening birth defect in humans. Total or partial anomalous pulmonary venous return (TAPVR or PAPVR) are significant causes of morbidity and mortality in childhood. Moreover, the pulmonary veins are prone to stenosis, which frequently complicates the treatment of patients with TAPVR and other forms of CHD. In addition, the pulmonary veins are a frequent site of origin for atrial arrhythmias in adults, and developmental abnormalities have been proposed to be at the root of such arrhythmias. Despite these clinically compelling conditions, development of the venous pole of the heart is a relatively understudied aspect of cardiovascular development. Semaphorins represent a class of signaling molecules that are critical in various developmental processes, including axon guidance, immune regulation, tumor angiogenesis and vascular patterning. Targeted mutation of Sema3D has results in TAPVR/PAPVR in mice. These mice present a novel tool for investigating the patterning of the pulmonary veins. Sema3D binds to neuropilin-1, and this interaction will be investigated in detail. As global deletion of Sema3D has a robust phenotype in mice, it is an excellent candidate gene for CHD in humans. A Sema3D missense mutation has been found in a patient with TAPVR. The functional impact of this mutation will be investigated and additional genetic analysis of patients is underway. The data obtained in the course of the proposed research will provide insights into normal and abnormal pulmonary venous patterning, semaphorin signaling, and the genetic roots of congenital heart disease.